1. Field of Invention
The present invention relates to a waveform recording system for electronifying and recording a prescribed input signal and indicating the waveform thereof on a display and, more particularly, to improvements in the display accuracy dependent on the relationship between the wave data and the compressed wave data.
2. Description of the Prior Art
Thanks to the recent dramatic increase in memory capacity, waveform recording systems have become capable of recording wave data over a prolonged period of time. As a result, however, the amount of data to be processed to replay waveforms has also become extremely large. To be able to quickly comprehend the whole image of wave data recorded over a long period, the system must meet the requirements for instantaneously making the wave data accessible as a single-frame view. In order to achieve this objective, a vast amount of wave data is previously compressed to produce compressed wave data. Then, the compressed wave data is saved in the memory, along with the original wave data.
When providing a single-frame view of the whole wave data, display image compression is performed according to the compressed wave data and, thus, display data is produced. Consequently, it is possible to display all measured waveforms in a short period of time. This logic is explained hereinafter with reference to the accompanying drawings.
FIG. 1 is a block diagram showing an example of the prior art waveform recording system.
In FIG. 1, an input of an analog wave signal to be measured is amplified and normalized by amp 3 using an appropriate gain applied to A/D converter 1, and digitized thereby for conversion to wave data. The wave data thus digitized by A/D-converter 1 is written to memory 4, as controlled by memory controller 2.
When providing the wave data thus written to memory 4 in a visual form, the wave data is retrieved as controlled by memory controller 2 and input to display image compressor 5, so that the data is compressed for display. Then, the compressed wave data is input to display 7 for display, as controlled by display controller 6. Display means 11 is comprised of display image compressor 5, display controller 6, and display 7.
Compression means 8 peak-to-peak (P-P) compresses the wave data digitized by A/D converter 1, on a channel-by-channel basis, at a compression ratio set in the compression means itself.
Upon receiving an input of the digitized wave data, compression means 8 calculates the maximum and minimum values contained in each prescribed number of wave data items that is set in real time in synchronization with the sampling rate of A/D converter 1. In other words, the compression means calculates “peak-to-peak (P-P) values” on a channel-by-channel basis.
For example, assuming that the compression ratio of compression means 8 is set to 1000, then the compression means outputs the maximum and minimum values once for 1000 items of wave data. Compression means 8 saves these maximum and minimum values, through memory controller 2, in an area other than the area of wave data in memory 4.
The compressed wave data, which is P-P compressed data provided by compression means 8, is stored in memory 4, through memory controller 2, along with the wave data digitized by A/D converter 1.
From among the items of wave data and compressed wave data stored in memory 4, specific data items are selected according to the preset display magnification and read through memory controller 2. Then, the data items are compressed by display image compressor 5 into display data. The display data thus compressed is sent to display controller 6 for visualization on display 7.
It should be noted that this example of the prior art system is described in Japanese Laid-open Patent Application 2002-111506.
As discussed above, it is possible to instantaneously display vast amounts of wave data saved in the memory.
In the prior art system, however, a trigger point is used as the reference point when acquiring and displaying wave data using a pre-trigger function. Therefore, the display start point of wave data does not always agree with the start point of an interval set off by a prescribed number of wave data items being compressed. Likewise, the end point of waveform display does not always agree with the endpoint of the compression interval. Consequently, disagreement occurs between the range of wave data for display and the range of wave data which is the origin of compressed wave data for display. It should be noted here that the term pre-trigger refers to a function in which a wave data item at a trigger point satisfying preset trigger conditions while wave data is being saved in the memory is used as the reference point, and waveforms for a prescribed period before and/or after the trigger point are displayed.
Also in the prior art system, there is the case that when wave data and compressed wave data stored in the memory are saved to another location or these data are analyzed on a different system, only the required parts thereof are copied from the memory to another medium. In this case, even if the wave data and compressed wave data are copied properly, an arbitrary range of the wave data is selected and, therefore, the range does not always agree with the range indicated by the start and end points of a compression interval. Consequently, the system has had the problem that disagreement occurs between the range of wave data that has been copied and the range of wave data which is the origin of the compressed wave data.